Implantable medical devices which deliver electrical stimulation to patient tissue, such as pacemakers, defibrillators and neurological stimulators, need to be able to transmit electrical pulses from electronic circuits within the implantable medical device while at the same time inhibiting bodily fluids from entering the implantable medical device and substances from leaving the implantable medical device to the extent possible. Electrical feedthroughs are commonly configured on such implantable medical devices to provide for the transmission of electrical pulses while also maintaining substantial or complete fluid isolation between the interior of the implantable medical device and the patient. Other implantable medical devices may utilize feedthroughs for other purposes providing an electrical ingress or egress to or from the implantable medical device or providing a throughput for some other therapeutic or diagnostic function. In addition, it is sometimes desirable for the feedthrough to contain a capacitor/filter assembly to reduce the amount of electromagnetic interference (EMI) entering the device.
Historically, implantable medical device feedthroughs have utilized a ferrule extending through a housing of the implantable medical device. An electrically conductive wire or pin is positioned within and extending through the ferrule and sealed to provide isolation. Such seals have typically incorporated a sealing member and gold preform rings and solder rings to bond the bulk to the pin and the ferrule.
Traditionally, while the gold has provided bonding while also being substantially biocompatible, the solder provides bonding which is inexpensive and easy to manipulate. In addition, gold and solder have, in the past, each been utilized because each has different bonding properties. While solder may bond easily to many substances, gold may have greater difficulty bonding or be incapable of bonding to certain substances to which solder may bond easily.
As a result of the different thermal properties of the different materials which have been utilized in the construction of feedthroughs, the manufacturing process for feedthroughs has involved a relatively large number of steps in comparison to the number of components. In particular, because the gold and solder have different melting points, each must be heated separately, resulting in twice the heating steps, with the resultant increase in manufacturing time, complexity and cost. Additionally, solder and gold each generally may have a different surface chemistry for bonding due to the large temperature offsets possibly resulting in increased in manufacturing steps.